Perhaps "available" is what you want: e.g., "The missing files might provide more information, but from the available documents we can conclude that ...."
it was more like a reply with humour, " there are no parts missing, there are parts .... (antonym for missing --- more than "available")
could it be = abound ?
"Abound" is a verb, meaning "to be present in large numbers." I wouldn't say it's an antonym of "missing," but you could probably make it work for your purposes.